1. Field of the Invention
The present invention generally relates to a valve timing control device for internal combustion engine that controls the opening/closing timings of engine intake and exhaust valves according to operating conditions of the engine.
2. Related Art
As is known in the internal combustion engine, the rotation of the crankshaft is conveyed via appropriate conveyance mechanism to the camshaft on which multiple cams are installed to open or close the multiple intake or exhaust valves in the engine. It is also known that the rotation ratio between the crankshaft and the camshaft is normally maintained at 2 to 1 via the conveyance mechanism.
However, the opening/closing timings of the intake and exhaust valves set via the crankshaft, conveyance mechanism and camshaft is set to the optimum timing of the corresponding internal combustion engine, such as for the rated output. However, if the opening/closing timings of these valves are fixed, the timings will slightly deviate during low loads or high loads of the engine, and abnormalities such as backflow of the exhaust gas may occur.
Thus, conventionally a rotational phase adjustment mechanism was placed between the conveyance means and the camshaft to adjust the mutual rotational phase or rotational phase between the crankshaft and the camshaft, and the opening/closing timings of said valves were variably controlled by the adjustment mechanism. For example, in the device described in Japanese Patent Application laid-open No. 2-308909, opening/closing timings of the valves were variably controlled with the following method:
An angle-wise synchronized signals were generated from both the crankshaft and the camshaft, PA1 The relative angle of rotation (opening/closing timing of valve, or valve timing) between the crankshaft and the camshaft were detected from the phase difference of these signals, PA1 While monitoring this relative angle of rotation, the phase adjustment amount by the rotational phase adjustment mechanism was fed back and controlled so valve opening/closing timings adapted to the operation conditions of the internal combustion engine could be achieved. PA1 (A) First computation means to compute the compensation value of the phase difference using one of the phase differences of the cam signal and the reference angle signal as the difference value or ratio value, and second computation means to compensate the phase difference of the cam signal and the reference angle signal phase difference other than that used as the reference by adding or multiplying each of the corresponding values of the computed compensation value, or PA1 (B) Phase difference compensation means in which compensation value computation means compute the difference amount value under the various operation conditions of the internal combustion engine using the compensation value for phase difference of the cam signal and the references angle signal as reference, a compensation value memory is incorporated in which computed compensation values are registered or stored as maps in correspondence to parameters that indicate the operation conditions of the internal combustion engine, and compensation means reads the corresponding compensation values from the compensation value memory according to each operation condition of the internal combustion engine for phase difference other than the cam signal and the reference angle signal phase difference not used as the reference. PA1 Means installed under installation conditions in which the position is deviated only the angle at which the camshaft angular velocity fluctuation can be absorbed at the position from the position corresponding angle-wise to the reference angle signal generated to the camshaft. PA1 Installed at uneven intervals under position conditions in which position is deviated only by angle in which the camshaft angular velocity fluctuation can be absorbed at position corresponding angle-wise to the reference angle signal in regard to row of cams having no angle-wise cycle looking from each camshaft axial direction.
The mechanism described in Japanese Patent Application laid-open No. 63-131808 is also known as the rotational phase adjustment mechanism. In this rotational phase adjustment mechanism, an intermediate member to convey the rotation by the engagement of a helical spline between the conveyance mechanism and the camshaft, and the rotational phase (relative angle of rotation) between the conveyance mechanism and the camshaft was varied by sliding this intermediate member from the hydraulic piston in the cam axial direction.
As explained below, the optimum opening/closing timing of the intake valve or exhaust valve changes according to the operation conditions of the internal combustion engine such as rotational speed and throttle opening degree. Thus, the device that controls the valve timing must swiftly respond to the changes in the engine conditions.
On the other hand, for the valve timing to be swiftly controlled by feed back in this manner, the valve timing detection cycle must be shortened, or in other words, multiple valve timings must be detected while the camshaft rotates once. For this, multiple signals that indicate the cam position (camshaft angle of rotation) must be generated while the camshaft rotates once.
However, normally the rotational angular velocity of the camshaft fluctuates because the force applied on the cam profile surface fluctuates due to the opening/closing drive of the valve. Thus, if multiple signals to indicate the cam position while the camshaft rotates once are generated, time-wise variations or inaccuracies will occur in the timing that the signals are generated due to this rotational angular velocity fluctuation. If this time-wise variation occurs in the signals for indicating the cams position, the detection results of the valve timing will fluctuate in synchronization with camshaft rotation.
In the rotational phase adjustment mechanism in which an intermediate member is engaged between the conveyance mechanism and the camshaft, various looseness will occur between the conveyance mechanism, the intermediate member and the camshaft. Thus, even if the adjustment mechanism is in the non-performing state, the intermediate member (engagement position of gears) will move the above looseness amount due to the fluctuation in the camshaft drive torque caused by the changes in the force applied on the cam profile surface. In other words, if the multiple signals for indicating the cam position are outputted, a differing phase difference will be indicated per signal for the reference angle signal generated based on the crankshaft rotation. This will also cause the detection results of the valve timing to fluctuate.
In this manner, if the detection results of the valve timing fluctuate, normally even if the above feedback control system is used, the rotation phase adjustment mechanism is controlled to absorb the fluctuation amount. This causes hunting to occur in the adjustment mechanism, and thus controlling to the target valve timing is difficult. This may also cause the feedback control reliability to be remarkably lost.
In the so-called V-type internal combustion engine, in which each cylinder block is divided into two banks with a V-shape centering on the crankshaft, two camshafts are installed, one for each bank, to operate the intake valves and exhaust valves. Each corresponding valve is sequentially driven via the independent cams installed on the two camshafts. Thus, often, the installation of the cam to the camshaft is itself non-cyclic, and although the fluctuation explained above is synchronized to the camshaft, it is not cyclic to each rotation of the camshaft. Thus, in the V-type internal combustion engine, if multiple signals are output to indicate the cam position, the rotational angular velocity fluctuation and drive torque fluctuation of the camshaft will be more serious.